well folks im having trouble with my 1985 3.4 and the problem appears to be stemming from the AED (auxillary enrichment device) this item seems to act as an auto choke and gives a richer air/ fuel mix when cold starting.

however i believe it to be on the blink and while the car is easy to start from cold it constantly runs rich as the aed is not "switching off" as a result its returning about 5mpg at best and running very lumpy at idle.

can i bypass this system easily so i can eliminate it from my enquiries so to speak?

and if so would it be prudent to leave it diconnected and revert to a manual choke set up? the car is constantly garaged in a warm environment and never left out so cold starting is the least of my concerns.

any advice would be deeply appreciated as im at my wits end with my beautiful car!

 

anybody any ideas?

 

These AEDs go back a very long way, (to the 60s Jaguars) and were always troublesome after a while, so a lot of people converted them to a manual switch on the dash rather than relying on the device to switch itself off when the engine warms up; I suggest you do too.

They do wear out as well, and replacements are quite expensive, but some spares can be purchased. AFAIK the only source is the Burlen Fuel Systems Company in England who also make the SU carburettors. This site also has technical information for users and repairers

AED UNIT | SU - The SU Carburetter Company

 

thank you for this info and the link you provided will prove invaluable! thanks again.

 

The AED is an On/Off device and as such never really good even when new. When I bought my first Jag (Series 1 XJ6) as a newish used car I connected the AED to a switch on the centre console. I learned to switch it off at the right time depending on ambient temp and driving conditions but had I kept it longer a manual conversion would have gone in.

 

got he aed overhauled by a specialist apparently the diaphragm had collapsed and allowed fuel to be dumped straight into the carbs, he also tuned it and overhauled the carbs and ignition ancillaries.........result===sweeet running xj.

 

Thanks for that. Nice to know you got the car running right at last. Hope it didn't cost too much for the AED overhaul.

The 3.4 litre engine was pretty trouble-free compared to the woes people got with the 4.2. I know, I had a 4.2 !!